This invention relates to a device for moderating the temperature of physiological or medical fluids. More particularly, this invention relates to the transfer bio-conduction of cold or hot energy from blood or other fluids before the blood or fluids are infused into a patient.
It is established that rapid infusion of cold blood and other cold fluids may cause a recipient's heart to stop. Complications caused by rapid infusion of cold blood or other fluids may be prevented by allowing the blood or fluid to warm as it passes through the delivery tubing on its way to the patient.
Rapid infusion of large amounts of fluid, plasma or blood, that are stored at low temperatures, approximately 4° C., can result in hypothermia. Patients at the greatest risk of infusible materials are the elderly, severely traumatized or with prolonged hypotension. Those who are undergoing open-heart surgery or abdominal surgery also suffer heat loss. The adverse effects of hypothermia include depressed myocardial function, increased hemoglobin oxygen affinity, and decreased hepatic metabolism of citrate. Direct infusion of 4° C. blood into the central circulation is dangerous. In cardiac surgery, a cardioplegic solution is used in an attempt to stop the heart, adding to the threat of imminent injury or death. It is known that hypothermia can adversely affect platelet function, the coagulation cascade and thus contributes to the bleeding associated with massive transfusion.
It is also known that during surgery blood and other fluids are heated to approximately body temperature of the patient. There are situations when inadvertently these fluids are warmed to a temperature in excess of the desired temperature (98-100° F.). The fluid at a high temperature may cause complications to the patient.
The prior art has tried to solve problems associated with the infusion of cold blood, which would result in hypothermia, and the infusion of warm blood, that is, over the temperature of 30° C., or other liquids by designing devices which have means for wrapping a tubing which carries blood or other fluid around a conducting unit, so that the unit may conduct cold or heat from the fluid passing through the tubes. Methods of warning often involve the use of electrical heat exchange coils. Other devices rely on the availability of AC/DC electrical current and need to be monitored.
U.S. Pat. No. 5,473,538 to Stihler et al. discloses an apparatus for heating fluids having a cylindrical heat exchanging body with outer grooves for holding a tubing or conduit through which the fluid flows. The groove for holding the tubing forms windings around the cylindrical body which emphasizes the number of windings per length of tubing for heat transfer. For example, with a fixed section length 1 to be warmed in the tubing, the heat transfer length L per winding W is at least increased by a factor of 1.4 or the heat-exchanging cylinder is directed largely horizontally and the diameter of the heat exchanging body is larger than or equal to 160 millimeters. This disclosure is limited to having a relatively large heat exchanging body so that the surface area of the tubing is in contact with it for a relatively long length of the tubing. This is required for heat transfer. More specifically, the length 1 per winding W assumes the value of at least 52 cm and the groove is fashioned in the vicinity of the opening from a heat insulating material or is coated with a heat insulating material.
The heat exchanging length 1 is defined as follows:1=π×dπw 
whereby d corresponds to the diameter of a straight circular cylinder minus twice the groove depth.
U.S. Pat. No. 5,370,674 issued to Farrell discloses a method of heating blood and fluid to a temperature appropriate for administration to a patient. The fluid is maintained at a desirable temperature during the procedure. The fluid in the tubing passes through an elasticized device incorporating a semi-solid composition with a relatively high heat capacity, which is preheated to the desired temperature for the fluid so that temperature transfer can take place prior to administration of the fluid to the patient.
U.S. Pat. No. 4,796,696, issued to Stockton et al., describes a heat exchange in the form of a hollow container. Catheters are placed inside the container adjacent to and touching the walls of a heat exchanger so that heat transfer may take place. The volume of the open area of the container is large, thereby allowing a significant amount of the tubing to be placed inside the container and heated.
U.S. Pat. No. 4,878,537, issued to Verkaart, discloses a heat exchanger used for heating physiological fluids which includes an inner tube, an outer tube, and a space between the two tubes for receiving a fluid. A warming fluid passes through the inner tube, which transfers through the tube to heat the fluid passing between the inner tube and the outer tube.
U.S. Pat. No. 3,612,059, issued to Ersek, describes a heat exchange fabricated to form a pair of thin flexible films bonded to form a pair of flow channels which are disposed in a parallel manner. On a top surface of the flexible film, there is a metallized reflective coating, and on the bottom is a black coating. Blood flows through the open channels formed by the pair of flexible films. The device is intended to be worn on the body of the patient and utilizes the patient's body heat for controlling the temperature of intravenous fluids being infused into the patient.
The disadvantage of conventional devices is that they may require the use of electricity to warm fluids for intravenous administration which are cumbersome and must be positioned close to the patient. Further, conventional tube-like pre-heated devices rapidly cool and after a short time are no longer effective. Other devices which may require the wrapping of flexible tubing in outer grooves are large and cumbersome. There is a need for a non-electrical, small diameter, liquid conductive cooling/heating device that is disposable and fits within one's hand for facile and convenient use.